Carbon dioxide (CO) electroreduction could provide a useful source of ethylene, but low conversion efficiency, low production rates, and low catalyst stability limit current systems. Here we report that a copper electrocatalyst at an abrupt reaction interface in an alkaline electrolyte reduces CO to ethylene with 70% faradaic efficiency at a potential of -0.55 volts versus a reversible hydrogen electrode (RHE). Hydroxide ions on or near the copper surface lower the CO reduction and carbon monoxide (CO)-CO coupling activation energy barriers; as a result, onset of ethylene evolution at -0.165 volts versus an RHE in 10 molar potassium hydroxide occurs almost simultaneously with CO production. Operational stability was enhanced via the introduction of a polymer-based gas diffusion layer that sandwiches the reaction interface between separate hydrophobic and conductive supports, providing constant ethylene selectivity for an initial 150 operating hours.

The electrochemical reduction of CO2 is a promising route to convert intermittent renewable energy to storable fuels and valuable chemical feedstocks. To scale this technology for industrial implementation, a deepened understanding of how the CO2 reduction reaction (CO2RR) proceeds will help converge on optimal operating parameters. Here, a techno‐economic analysis is presented with the goal of identifying maximally profitable products and the performance targets that must be met to ensure economic viability—metrics that include current density, Faradaic efficiency, energy efficiency, and stability. The latest computational understanding of the CO2RR is discussed along with how this can contribute to the rational design of efficient, selective, and stable electrocatalysts. Catalyst materials are classified according to their selectivity for products of interest and their potential to achieve performance targets is assessed. The recent progress and opportunities in system design for CO2 electroreduction are described. To conclude, the remaining technological challenges are highlighted, suggesting full‐cell energy efficiency as a guiding performance metric for industrial impact.

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We report on the achievement of wafer-level photocatalytic overall water splitting on GaN nanowires grown by molecular beam epitaxy with the incorporation of Rh/Cr(2)O(3) core-shell nanostructures acting as cocatalysts, through which H(2) evolution is promoted by the noble metal core (Rh) while the water forming back reaction over Rh is effectively prevented by the Cr(2)O(3) shell O(2) diffusion barrier. The decomposition of pure water into H(2) and O(2) by GaN nanowires is confirmed to be a highly stable photocatalytic process, with the turnover number per unit time well exceeding the value of any previously reported GaN powder samples.

The electroreduction of CO2 to CO is a promising strategy to utilize CO2 emissions while generating a high value product.